Robert E. Hodges, Department of Geography, The Florida State University, Tallahassee, FL; and J. B. Elsner

The relationship between USA hurricanes and solar activity is investigated empirically. First a relationship between the probability of a USA hurricane and the solar cycle is shown that is conditional on ocean temperature. For years of above normal ocean temperatures, the probability of three or more USA hurricanes decreases from 40% to 20% as sunspot numbers increase from the lower to the upper quartiles. Second, since ocean temperatures are in phase with the 11-year total solar irradiance cycle but upper-level atmospheric temperatures are in phase with ultraviolet radiation changes on the monthly time scale, an index is constructed that tracks intra hurricane-season changes in solar activity. The index is inversely related to the total sunspot numbers and is significantly correlated with USA hurricanes and major USA hurricanes over the period 1851–2008. The chances of at least one hurricane affecting the USA in the lowest and highest SSN anomaly season are 25% and 64%, respectively. A similar relationship is noted using older hurricane records that predate the official dataset providing independent corroborating evidence linking solar variability with the probability of a USA hurricane.